The present invention generally relates to improved discrete parts, such as fasteners, having a useful barrier coating applied to a portion thereof and a method and apparatus for processing such parts with a coating material. More particularly, the invention relates to the deposition of liquid fluorocarbon or hydrocarbon type coating materials in a precise and continuous high speed manner onto selected surfaces of fasteners to form a masking insulating and/or lubricating barrier coating on the fasteners. A particular application of the invention is the application of liquid fluorocarbon coating material to the internal threads and possibly other surfaces of an odd shaped nut having a deep threaded central hub.
Metal parts such as fasteners are being increasingly exposed to electrodeposition paints, primers, and corrosion resistant materials. Recent advances in improving the corrosion resistance of automobile bodies and other like structures have made use of such formulations for the treatment of steel structural members standards in industry. Many fastening elements are attached to basic structural components prior to processing of such components with electrodeposited primers, paints, and rust inhibitors. Therefore, any exposed threads of the fasteners attached to such components may become contaminated and make it difficult or impossible to thread such exposed fasteners with a mating fastener for subsequent assembly. Any coatings applied to such fasteners to resist contamination must also be sufficient to resist splatter from the welding procedures that they may be exposed to as they are affixed to the structural components. The need, therefore, arose to develop a way of preventing contamination of these exposed fastener threads that would not substantially interfere with the ultimate performance of such fasteners.
The prior art proposed a variety of coating systems to attempt to solve the problem of resisting corrosion inhibitor build-up on the threads of fasteners. However, these prior coating systems all suffered from substantial drawbacks even when used to coat standard types of fasteners. This has led to the development of improved coating methods and apparatus utilizing liquid fluorocarbon coating materials, such as described in applicants' copending application Ser. No. 08/483,100 filed Jun. 7, 1995. Such new systems feature capabilities that have caused demand for such coatings on a wide variety of different types of fasteners and other discrete parts to continue to increase. The expanding popularity of such coatings has further compounded the challenges facing existing coating systems.
For example, there has been increasing demand in industry for providing coatings on various odd shaped fasteners to resist the build-up of electrodeposited paints, primers, and corrosion resistant materials. These fasteners include, for example, internally threaded fasteners with extended hub sections, internally threaded fasteners with rounded lead in sections between the top surface of the fastener and the threaded portion, fasteners having off center openings and fasteners that have significantly different top surfaces than bottom surfaces.
Further compounding the difficulties of depositing a suitable barrier coating on such fasteners has been an increase in the need to cover not just threaded portions of such fasteners, but also all or a portion of other surfaces such as lead in sections or top or bottom face portions of the fastener at the same time. Specifications requiring such extended coating coverage necessitate very precise control so that only certain predesignated portions of the threads and additional parts of the fastener are coated while the remainder of the fastener remains free of such barrier coatings.
The vast majority of prior art systems are incapable of accommodating irregular types or shapes of fasteners or achieving the coating of a combination of fastener surfaces described above. U.S. Pat. No. 4,842,890 to Sessa et al. discloses a method for coating fasteners with a powdered fluorocarbon material. This method, however, is restricted to coating fasteners that have a head and shank port ion and cannot accommodate either internally threaded fasteners or odd shaped fasteners.
U.S. Pat. No. 4,652,468 to Gould et al. discloses a process for high pressure impact coating of threaded openings of internally threaded fasteners with fluorocarbon materials such as Teflon.RTM.. The Gould process attempts to specifically avoid the deposition of coating material on any surfaces of the fastener other than the threads. The process requires a masking of the surfaces of a nut in order to restrict the coating material from being applied to any other surfaces of the nut.
This process is complicated and expensive because it requires a choked area for drawing in the excess coating material from the opening of the nut and necessitates indexing, masking, and removing excess material during the coating process in a manner that significantly slows processing speeds. Additionally, Gould does not teach a way of accommodating any odd shaped internally threaded fasteners.
U.S. Pat. No. 4,701,348 to Neville discloses a method of coating the threads of internally threaded fasteners. Neville requires a metering nozzle to be selectively introduced and removed from a succession of internally threaded fasteners. The reciprocating movement of the nozzle necessitates an indexing fasteners that stops the flow of fasteners each time coating material is being applied to any single fastener. This dramatically slows processing rates.
The Neville nozzle has an ultrasonic tip which is vibrated after the metering of a drop of coating material in order to explode the drop to cause a fine mist of the fluid suspension to be sent towards the threads of the nut. Due to the difficulty in metering identically sized drops and successions exploding in the exact same manner using an ultrasonic power source. This system often exhibits uneven coating of the fasteners. Additionally, the flat, continuous belt and nozzle construction of Neville do not allow odd sized fasteners to be processed, nor is the coating of any portion other than the threads of the fastener contemplated.
Published PCT International Application WO8906757 of Prittinen et al. discloses a method and apparatus for coating internally threaded fasteners with materials such as Teflon.RTM.. This invention provides an indexed flow of fasteners before an application device that introduces a reciprocating rotary probe into each fastener to be coated. In addition to being slow because of the indexing required, this device does not contemplate application of Teflon.RTM. materials to any surfaces other than threads the fastener. This system also lacks a supporting structure that can readily and easily accommodate various different types of odd sized fasteners.
Furthermore, most of the prior art systems identified above require post application heat treatment of the coated fasteners, such as by baking in an oven. None of these references describes any type of on-line device or method for efficiently and simply moving the coated fasteners from the application conveyor to a post application heating station, such as an oven. Instead these systems deposited coated fasteners into bins or racks which then had to be physically brought to an oven and manually unloaded. As can be readily appreciated, this process was very labor intensive.
It is, therefore, apparent that a need exists in the art for an improved apparatus and method of coating the threads and/or other portions of a wide variety of fasteners to prevent electrodeposition of paints or corrosion resistant materials and for an improved on-line system of transferring coated fasteners into a post application heating station.